• Journal of the Korean Electrochemical Society
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• v.23 no.2
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• pp.25-38
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• 2020

Photoelectrochemical water splitting has been considered as the most promising technology for generating hydrogen energy. Transition metal dichalcogenide (TMD) compounds have currently attracted tremendous attention due to their outstanding ability towards the catalytic water-splitting hydrogen evolution reaction (HER). Herein, we report the synthesis method of various transition metal dichalcogenide including MoS₂, MoSe₂, WS₂, and WSe₂ nanosheets as excellent catalysts for solar-driven photoelectrochemical (PEC) hydrogen evolution. Photocathodes were fabricated by growing the nanosheets directly onto Si nanowire (NW) arrays, with a thickness of 20 nm. The metal ion layers were formed by soaking the metal chloride ethanol solution and subsequent sulfurization or selenization produced the transition metal chalcogenide. They all exhibit excellent PEC performance in 0.5 M H₂SO₄; the photocurrent reaches to 20 mA cm^-2 (at 0 V vs. RHE) and the onset potential is 0.2 V under AM1.5 condition. The quantum efficiency of hydrogen generation is avg. 90%. The stability of MoS₂ and MoSe₂ is 90% for 3h, which is higher than that (80%) of WS₂ and WSe₂. Detailed structure analysis using X-ray photoelectron spectroscopy for before/after HER reveals that the Si-WS₂ and Si-WSe₂ experience more oxidation of Si NWs than Si-MoS₂ and Si-MoSe₂. This can be explained by the less protection of Si NW surface by their flake shape morphology. The high catalytic activity of TMDs should be the main cause of this enhanced PEC performance, promising efficient water-splitting Si-based PEC cells.

• Korean Journal of Environment and Ecology
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• v.30 no.6
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• pp.1022-1031
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• 2016

Relationships of standing biomass with biodiversity and structural diversity were examined in the Quercus mongolica-dominated forest in Mt. Jeombong, Gangwon-do. We examined the standing biomass of the Q. mongolia community ($311.1ton{\cdot}ha^{-1}$) from 2004 to 2013, and the observed major species were Q. mongoilca, Carpinus cordata, Tilia amurensis whose standing biomasses were $206.3ton{\cdot}ha^{-1}$ (66.3%), $36.9ton{\cdot}ha^{-1}$ (11.9%), and $30.6ton{\cdot}ha^{-1}$ (9.8%), respectively. Although the number of Q. mongolica individuals was very small compared with total density, the reason that Q. mongolica showed the most biomass than other species is due to greater average diameter at breast height (DBH) and the higher number of $DBH{\geq}50cm$ individuals. We calculated the range of Shannon index (H') and Shannon evenness (J') in the Q. mongolica community, and they were gradually increased in time, showing 2.015~2.166, 0.673~0.736, respectively. Their H' and J' showed positive linear relationships with their standing biomass. This indicates that the spatial distribution of the standing biomass in Q. mongoilca community becomes more homogeneous with time and this homogenization appears in various species in the community. In addition, we estimated biomass-species index (BS) and abundance-biomass-speciesdiversity (ABS) and they also showed gradual increase in time, ranging from 3.746 to 3.811 and from 4.781 to 5.028, respectively. Their indices showed positive linear relationships with the standing biomass. This can be explained from the observations of variations in standing biomass with tree diameters as the differences in the average standing biomass in the community have reduced gradually in time. Moreover, it is expected that increase in the structure diversity of the Q. mongoilca community enhances the efficiency in carbon sequestration and productivity, so the community can be developed to a more sustainable ecosystem with more abundant resources. Thus, applications of uneven-aged plantations with considerations of local ecological properties can be a very efficient reforestation method to ensure stable support of biodiversity and productivity.

• Journal of Korea Water Resources Association
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• v.53 no.1
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• pp.15-27
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• 2020

Streamflow discharge as a fundamental riverine quantity plays a crucial role in water resources management, thereby requiring accurate in-situ measurement. Recent advances in instrumentations for the streamflow discharge measurement has complemented or substituted classical devices and methods. Among various potential methods, surface current meter using microwave has increasingly begun to be applied not only for flood but also normal flow discharge measurement, remotely and safely enabling practitioners to measure flow velocity postulating indirect contact. With minimized field preparedness, this method facilitated and eased flood discharge measurement in the difficult in-situ conditions such as extreme flood in active ways emitting 24.125 GHz microwave without relying on natural lights. In South Korea, a rectangular shaped instrument named with Microwave Water Surface Current Meter (MWSCM) has been developed and commercially released around 2010, in which domestic agencies charging on streamflow observation shed lights on this approach regarding it as a potential substitute. Considering this brand-new device highlighted for efficient flow measurement, however, there has been few noticeable efforts in systematic and comprehensive evaluation of its performance in various measurement and riverine conditions that lead to lack in imminent and widely spreading usages in practices. This study attempted to evaluate the MWSCM in terms of instrumen's monitoring configuration particularly regarding tilt and yaw angle. In the middle of pointing the measurement spot in a given cross-section, the observation campaign inevitably poses accuracy issues related with different tilt and yaw angles of the instrument, which can be a conventionally major source of errors for this type of instrument. Focusing on the perspective of instrument configuration, the instrument was tested in a controlled outdoor river channel located in KICT River Experiment Center with a fixed flow condition of around 1 m/s flow speed with steady flow supply, 6 m of channel width, and less than 1 m of shallow flow depth, where the detailed velocity measurements with SonTek micro-ADV was used for validation. As results, less than 15 degree in tilting angle generated much higher deviation, and higher yawing angle proportionally increased coefficient of variance. Yaw angles affected accuracy in terms of measurement area.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.6
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• pp.1297-1308
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• 2015

In Korea, the local traffic safety master plan has been established and implemented according to the Traffic Safety Act. Each local government is required to establish a customized traffic safety policy and share roles for improvement of traffic safety and this means that local governments lead and promote effective local traffic safety policies fit for local circumstances in substance. For implementing efficient traffic safety policies, which accord with many-sided characteristics of local governments, the prediction of community-based traffic accidents, which considers local characteristics and the analysis of accident influence factors must be preceded, but there is a shortage of research on this. Most of existing studies on the community-based traffic accident prediction used social and economic variables related to accident exposure environments in countries or cities due to the limit of collected data. For this reason, there was a limit in applying the developed models to the actual reduction of traffic accidents. Thus, this study developed a local traffic accident prediction model, based on smaller regional units, administrative districts, which were not omitted in existing studies and suggested a method to reflect traffic safety facility and policy variables that traffic safety policy makers can control, in addition to social and economic variables related to accident exposure environments, in the model and apply them to the development of local traffic safety policies. The model development result showed that in terms of accident exposure environments, road extension, gross floor area of buildings, the ratio of bus lane installation and the number of crossroads and crosswalks had a positive relation with accidents and the ratio of crosswalk sign installation, the number of speed bumps and the results of clampdown by police force had a negative relation with accidents.

• The korean journal of orthodontics
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• v.29 no.5 s.76
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• pp.551-562
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• 1999

This study was undertaken to investigate the relation between orthodontic force magnitude and the amount of tooth movement. And more light force application for reducing root resorption Twenty-four rats were divided into three experimental groups(A, B, C) based on force magnitude and application method. Springs of 50g force were applied to A group, springs of 100g force were applied to B group and springs of 25g force were applied to C group initially, and after 4 days springs of C group were changed to springs of 50g force. Two kinds of $sentally^{(R)}$(GAC U.S.A.) closed coil spring, 50g and 100g, were used. And we made 25g springs by heat treatment process of 50g springs. Each spring was inserted between the maxillary central incisor and the maxillary left first molar. Amounts of tooth movement were measured everyday by digital caliper($Digimatic^{(R)}$, Mitutoyo, Japan) under inhalation anesthesia for 15 days. After 15 days, all rats were sacrificed and histological samples were obtained with Hematoxyline-Eosin stain and Masson's trichrome stain. Following conclusion were made; 1. Group B showed the mean cumulative tooth movement of $2.19{\pm}0.41mm$ at 15th day, which was greatest among three groups, followed by group C($2.06{\pm}0.10mm$), group A($1.90{\pm}0.49mm$) respectively. however, there was no statistically difference among three groups. 2. All groups showed general tooth movement pattern and A, B, C group finished lag phase at 9th, 8th, 7th day, but there was no statistical significance. 3. Group A,B,C showed root resorption and especially group B showed the most severe root resorption and group C showed milder root resorption than other groups. According to the above results, large initial force with the development of a flirty widespread hyalinized zone may cause severe root resorption, so initial force should be applied lightly to reduce hyalinized area and eventually root resorption and then increased force will induce efficient tooth movement.

• Clinical and Experimental Reproductive Medicine
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• v.30 no.1
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• pp.39-45
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• 2003

Objective : To identify the factors affecting the complete fetal loss following multifetal pregnancy reduction (MFPR). Design: Retrospective clinical study. Methods : A total of 256 consecutive treatments of MFPR in IVF-ET cycles performed between 1992 through 2000 in Samsung Cheil hospital were analyzed. MFPR was done around 8 weeks of gestation by transvaginal ultrasono-guided aspiration in multiple pregnancies and reduced to singleton or twins. Stepwise logistic regression was performed to identify the factors affecting the final outcome of pregnancy after MFPR. Dependent variable was complete fetal loss and the independent variables were maternal age, paternal age, initial number of gestational sac (iGSNO), initial number of fetal heart beat, the number of remaining live fetus after MFPR, and chorionicity. Results: The total survival rate was 87.9%, and total fetal loss rate after MFPR was 12.1%. Total fetal loss occurred within four weeks from MFPR procedure was 1.95%. Total loss occurred after four weeks of procedure and before 24 gestational weeks was 8.2%. Seventy nine percent (202/256) of pregnancies delivered after 34 weeks of gestation. The survival rate of pregnancies reduced to singleton was significantly higher than that of pregnancies reduced to twins (93.5% vs. 86.7%, p<0.05). The mean ($\pm$SEM) gestational age at delivery was $36.2{\pm}1.0$ and $34.1{\pm}0.5$ weeks for pregnancies reduced to singletons and twins, respectively (p=0.065). Logistic regression analysis revealed that the maternal age, the number of initial gestational sac (iGSNO), and the number of remaining live fetus after MFPR significantly affected the rate of total fetal loss (Z = 0.174'age + 0.596'iGSNO + 1.324'remaining fetuses -12.07), (p<0.05). Conclusions: MFPR seems to be a relatively safe and efficient method to improve the obstetric outcome in high order multiple pregnancy. Because the maternal age, the number of initial gestational sac and the remaining live fetuses after MFPR affect the total fetal loss rate, restriction of the number of transferred embryos according to the age and MFPR to singleton fetus could be considered for the better obstetric outcome in IVF pregnancy.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.1
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• pp.1-10
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• 2005

The purpose of this study was to evaluate the potential of a gamma irradiation to decompose 2,4,6-trinitrotoluene(TNT) in an aqueous solution. The decomposition reaction of TNT by gamma irradiation was a pseudo first-order kinetic over the applied initial concentrations($25{\sim}100mg/L$). The dose constant was strongly dependent on the initial TNT concentration. The removal of TNT was more efficient at pH below 3 and at pH above 11 than at neutral pH(pH 5-9). The required irradiation dose to remove over 99% of TNT was 40, 80 and 10 kGy, individually at pH 2, 7 and 13. The dose constant was increased by 1.6 fold and over 15.6 fold at pH 2 and 13, respectively, when compared with that at pH 7 When irradiation dose of 200 kGy was applied, the removal efficiencies of TOC were 91, 46 and 53% at pH 2, 7 and 13, respectively. Ammonia and nitrate were detected as the main nitrogen byproducts of TNT and glyoxalic acid and oxalic acid were detected as organic byproducts. The results showed that a gamma irradiation was an attractive method for the decomposition of TNT in an aqueous solution. However, regarding the application of high energy radiation for the TNT decomposition and mineralization, an application of an acidic pH below 3 to the solution before irradiation should be considered.

• The korean journal of orthodontics
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• v.30 no.2 s.79
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• pp.205-214
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• 2000

Recently, the magnetic force has been considered as a method for a more efficient tooth movement. The purpose of this study was to evaluate the effects of different static magnetic fields of Nd-Fe-B magnet on MC3T3-E1 cells by measuring the alkaline phosphatase activity and observing the amount of stained alkaline phosphatase. For measuring of alkaline phosphatase activity, MC3T3-E1 cells were seeded in first and third row of 12 well culture plates. And Nd-Fe-B magnets were positioned under the first column of first and third row to apply different static magnetic fields(first column:100mT ; second column:4.6mT ; third column:0.5mT ; forth column:0.0mT) to the cells for 7, 13, 19, and 25 days. For staining of alkaline phosphatase, MC3T3-E1 cells were seeded in 100mm culture plates. And Nd-Fe-B magnets were positioned under the corner of plates to apply different static magnetic fields(magnet side:100mT : the opposite side:0.5mT) to the cells for 7, 13, 19, and 25 days. The results were as follows : 1. ALP activity was increased until day 19 in biochemical determination as well as in histochemical staining, 2. The application of higher magnetic field(100mT) suppressed ALP activity at day 13, 19, 25. On the contrary, the application of the lower magnetic field(4.6mT, 0.5mT) significantly enhanced the ALP activity. 3. Consistent with enzyme assay, histochemical staining of ALP also demonstrated that higher magnetic field(100mT) suppressed ALP activity, lower one(0.5mT) enhanced.

• The korean journal of orthodontics
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• v.39 no.4
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• pp.213-224
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• 2009

Objective: The aim of this study was to find out whether Er:YAG laser can aid in debonding ceramic brackets, and to see what kind of method will be the most appropriate for debonding. Methods: One hundred and ninety teeth, monocrystalline brackets ($MISO^{TM}$, HT, Ansan-Si, Korea), polycrystalline brackets ($Transcend^{TM}$ series 6000, 3M Untek, Monrovia, CA, USA) and the KEY Laser3 (KavoDental, Biberach, Germany) were used. Experimental groups were classified according to the type of ceramic brackets, and the amount of laser energy (0, 140, 300, 450, 600 mJ). After applying laser on the bracket at two points at 1 pulse each, the shear bond strength was measured. The effect of heat caused by laser was measured at the enamel beneath the bracket and pulp chamber. After measuring the shear bond strength, adhesive residue was evaluated and enamel surface was investigated using SEM. Results: All ceramic bracket groups showed a significant decrease in shear bond strength as the laser energy increased. The greatest average temperature change was $3.78^{\circ}C$ on the enamel beneath the bracket and $0.9^{\circ}C$ on the pulp chamber. Through SEM, crater shape holes caused by the laser was seen on the enamel and adhesive surfaces. Conclusions: If laser is applied on ceramic brackets for debonding, 300 - 450 mJ of laser energy will be safe and efficient for monocrystalline brackets ($MISO^{TM}$), and about 450 mJ for polycrystalline brackets ($Transcend^{TM}$ series 6000).

• Journal of The Korean Association For Science Education
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• v.32 no.1
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• pp.30-45
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• 2012

Educational communities around the world have concentrated on integrative efforts among science, technology, engineering and mathematics (Science, Technology, Engineering, and Mathematics: STEM) subjects. Korea has focused on integrative education among STEAM (Science, Technology, Engineering, Arts, and Mathematics) school subjects to raise talented human resources in the fields of science and technology. The purpose of this study was to analyze secondary school science, technology, and mathematics teacher's perceptions and needs toward integrated education and integrative STEM education. A total of 251 secondary school teachers from all areas of the country who have taught science, mathematics, and technology were surveyed by using a self-reported instrument. The findings were as follows: First, teachers have used little integrated education in their classes due to insufficient time in the actual preparation of the integrated education and the lack of expertise, teaching experience, and teaching-learning materials for the integrated education, while they have positive thoughts about the need of integrated education. Second, they presented several needs to facilitate the integrated education: development of a variety of integrated programs, school administrative and financial support, and in-service teachers' training. Third, overall perception toward integrated STEM education was not sufficient, but most teachers perceived the need toward integrated STEM education due to students' development in their creativity, thinking skills, and adaptability. Fourth, they perceived that it was imperative to develop the various integrated STEM education programs, distribute the materials, and help STEM teachers' understanding toward integrated STEM education. Fifth, they perceived that the most relevant method to integrate STEM subjects was the problem solving approach. In addition, they appreciate that the integrated STEM education is highly efficient in not only developing integrated problem solving skills and STEM related literacy, but also in positively impacting the rise of talented human resources in the fields of science and technology. In order to increase the awareness of STEM-related secondary school teachers and vitalize the integrated STEM education, it is necessary to develop and spread a variety of programs, effective teaching and learning materials, and teachers' training programs.